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</head>
<body class="article">
<div id="header">
<h1>Spring WebFlux Workshop</h1>
<div class="details">
<span id="author" class="author">Brian Clozel, Violeta Georgieva - Pivotal</span><br>
</div>
<div id="toc" class="toc">
<div id="toctitle">Table of Contents</div>
<ul class="sectlevel1">
<li><a href="#_stock_quotes_application">Stock Quotes application</a>
<ul class="sectlevel2">
<li><a href="#_create_this_application">Create this application</a></li>
<li><a href="#_create_a_quote_generator">Create a Quote Generator</a></li>
<li><a href="#_functional_web_applications_with_webflux_fn">Functional web applications with "WebFlux.fn"</a></li>
<li><a href="#_create_your_first_handlerfunction_routerfunction">Create your first HandlerFunction + RouterFunction</a></li>
<li><a href="#_expose_the_flux_quotes_as_a_web_service">Expose the Flux&lt;Quotes&gt; as a web service</a></li>
<li><a href="#_integration_tests_with_webtestclient">Integration tests with WebTestClient</a></li>
</ul>
</li>
<li><a href="#_trading_service_application">Trading Service application</a>
<ul class="sectlevel2">
<li><a href="#_create_this_application_2">Create this application</a></li>
<li><a href="#_use_tomcat_as_a_web_engine">Use Tomcat as a web engine</a></li>
<li><a href="#_use_a_reactive_datastore">Use a reactive datastore</a></li>
<li><a href="#_create_a_json_web_service">Create a JSON web service</a></li>
<li><a href="#_use_thymeleaf_to_render_html_views">Use Thymeleaf to render HTML views</a></li>
<li><a href="#_use_the_webclient_to_stream_json_to_the_browser">Use the WebClient to stream JSON to the browser</a></li>
<li><a href="#_create_and_configure_a_websockethandler">Create and Configure a WebSocketHandler</a></li>
<li><a href="#_integration_tests_with_websocketclient">Integration tests with WebSocketClient</a></li>
</ul>
</li>
<li><a href="#_additional_resources">Additional Resources</a></li>
</ul>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>This repository hosts a complete workshop on Spring Boot + Spring WebFlux.
Just follow this README and create your first WebFlux applications!
Each step of this workshop has its companion commit in the git history with a detailed commit message.</p>
</div>
<div class="paragraph">
<p>We&#8217;ll create two applications:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>stock-quotes</code> is a functional WebFlux app which streams stock quotes</p>
</li>
<li>
<p><code>trading-service</code> is an annotation-based WebFlux app using a datastore, HTML views, and several browser-related technologies</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Reference documentations can be useful while working on those apps:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="http://projectreactor.io/docs">Reactor Core documentation</a></p>
</li>
<li>
<p>Spring WebFlux
<a href="http://docs.spring.io/spring-framework/docs/5.0.6.RELEASE/spring-framework-reference/web-reactive.html#spring-webflux">reference documentation</a>
and <a href="http://docs.spring.io/spring-framework/docs/5.0.6.RELEASE/javadoc-api/">javadoc</a></p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_stock_quotes_application"><a class="anchor" href="#_stock_quotes_application"></a>Stock Quotes application</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_create_this_application"><a class="anchor" href="#_create_this_application"></a>Create this application</h3>
<div class="paragraph">
<p>Go to <code><a href="https://start.spring.io" class="bare">https://start.spring.io</a></code> and create a Maven project with Spring Boot 2.0.2.RELEASE,
with groupId <code>io.spring.workshop</code> and artifactId <code>stock-quotes</code>. Select the <code>Reactive Web</code>
Boot starter.
Unzip the given file into a directory and import that application into your IDE.</p>
</div>
<div class="paragraph">
<p>If generated right, you should have a main <code>Application</code> class that looks like this:</p>
</div>
<div class="listingblock">
<div class="title">stock-quotes/src/main/java/io/spring/workshop/stockquotes/StockQuotesApplication.java</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-java" data-lang="java">package io.spring.workshop.stockquotes;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class StockQuotesApplication {

	public static void main(String[] args) {
		SpringApplication.run(StockQuotesApplication.class, args);
	}
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>Edit your <code>application.properties</code> file to start the server on a specific port.</p>
</div>
<div class="listingblock">
<div class="title">stock-quotes/src/main/resources/application.properties</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-properties" data-lang="properties">server.port=8081</code></pre>
</div>
</div>
<div class="paragraph">
<p>Launching it from your IDE or with <code>mvn spring-boot:run</code> should start a Netty server on port 8081.
You should see in the logs something like:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-bash" data-lang="bash">INFO 2208 --- [  restartedMain] o.s.b.web.embedded.netty.NettyWebServer  : Netty started on port(s): 8081
INFO 2208 --- [  restartedMain] i.s.w.s.StockQuotesApplication           : Started StockQuotesApplication in 1.905 seconds (JVM running for 3.075)</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_create_a_quote_generator"><a class="anchor" href="#_create_a_quote_generator"></a>Create a Quote Generator</h3>
<div class="paragraph">
<p>To simulate real stock values, we&#8217;ll create a generator that emits such values at a specific interval.
Copy the following classes to your project.</p>
</div>
<div class="listingblock">
<div class="title">stock-quotes/src/main/java/io/spring/workshop/stockquotes/Quote.java</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-java" data-lang="java">package io.spring.workshop.stockquotes;

import java.math.BigDecimal;
import java.math.MathContext;
import java.time.Instant;

public class Quote {

	private static final MathContext MATH_CONTEXT = new MathContext(2);

	private String ticker;

	private BigDecimal price;

	private Instant instant;

	public Quote() {
	}

	public Quote(String ticker, BigDecimal price) {
		this.ticker = ticker;
		this.price = price;
	}

	public Quote(String ticker, Double price) {
		this(ticker, new BigDecimal(price, MATH_CONTEXT));
	}

	public String getTicker() {
		return ticker;
	}

	public void setTicker(String ticker) {
		this.ticker = ticker;
	}

	public BigDecimal getPrice() {
		return price;
	}

	public void setPrice(BigDecimal price) {
		this.price = price;
	}

	public Instant getInstant() {
		return instant;
	}

	public void setInstant(Instant instant) {
		this.instant = instant;
	}

	@Override
	public String toString() {
		return "Quote{" +
				"ticker='" + ticker + '\'' +
				", price=" + price +
				", instant=" + instant +
				'}';
	}
}</code></pre>
</div>
</div>
<div class="listingblock">
<div class="title">stock-quotes/src/main/java/io/spring/workshop/stockquotes/QuoteGenerator.java</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-java" data-lang="java">package io.spring.workshop.stockquotes;

import java.math.BigDecimal;
import java.math.MathContext;
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;

import reactor.core.publisher.Flux;

import org.springframework.stereotype.Component;

@Component
public class QuoteGenerator {

	private final MathContext mathContext = new MathContext(2);

	private final Random random = new Random();

	private final List&lt;Quote&gt; prices = new ArrayList&lt;&gt;();

	/**
	 * Bootstraps the generator with tickers and initial prices
	 */
	public QuoteGenerator() {
		this.prices.add(new Quote("CTXS", 82.26));
		this.prices.add(new Quote("DELL", 63.74));
		this.prices.add(new Quote("GOOG", 847.24));
		this.prices.add(new Quote("MSFT", 65.11));
		this.prices.add(new Quote("ORCL", 45.71));
		this.prices.add(new Quote("RHT", 84.29));
		this.prices.add(new Quote("VMW", 92.21));
	}


	public Flux&lt;Quote&gt; fetchQuoteStream(Duration period) {

		// We want to emit quotes with a specific period;
		// to do so, we create a Flux.interval
		return Flux.interval(period)
				// In case of back-pressure, drop events
				.onBackpressureDrop()
				// For each tick, generate a list of quotes
				.map(this::generateQuotes)
				// "flatten" that List&lt;Quote&gt; into a Flux&lt;Quote&gt;
				.flatMapIterable(quotes -&gt; quotes)
				.log("io.spring.workshop.stockquotes");
	}

	/*
	 * Create quotes for all tickers at a single instant.
	 */
	private List&lt;Quote&gt; generateQuotes(long interval) {
		final Instant instant = Instant.now();
		return prices.stream()
				.map(baseQuote -&gt; {
					BigDecimal priceChange = baseQuote.getPrice()
							.multiply(new BigDecimal(0.05 * this.random.nextDouble()), this.mathContext);
					Quote result = new Quote(baseQuote.getTicker(), baseQuote.getPrice().add(priceChange));
					result.setInstant(instant);
					return result;
				})
				.collect(Collectors.toList());
	}

}</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_functional_web_applications_with_webflux_fn"><a class="anchor" href="#_functional_web_applications_with_webflux_fn"></a>Functional web applications with "WebFlux.fn"</h3>
<div class="paragraph">
<p>Spring WebFlux comes in two flavors of web applications: annotation based and functional.
For this first application, we&#8217;ll use the functional variant.</p>
</div>
<div class="paragraph">
<p>Incoming HTTP requests are handled by a <code>HandlerFunction</code>, which is essentially a function
that takes a ServerRequest and returns a <code>Mono&lt;ServerResponse&gt;</code>. The annotation counterpart
to a handler function would be a Controller method.</p>
</div>
<div class="paragraph">
<p>But how those incoming requests are routed to the right handler?</p>
</div>
<div class="paragraph">
<p>We&#8217;re using a <code>RouterFunction</code>, which is a function that takes a <code>ServerRequest</code>, and returns
a <code>Mono&lt;HandlerFunction&gt;</code>. If a request matches a particular route, a handler function is returned;
otherwise it returns an empty <code>Mono</code>. The <code>RouterFunction</code> has a similar purpose as the <code>@RequestMapping</code>
annotation in <code>@Controller</code> classes.</p>
</div>
<div class="paragraph">
<p>Take a look at the code samples in
<a href="http://docs.spring.io/spring-framework/docs/5.0.6.RELEASE/spring-framework-reference/web.html#web-reactive-server-functional">the Spring WebFlux.fn reference documentation</a></p>
</div>
</div>
<div class="sect2">
<h3 id="_create_your_first_handlerfunction_routerfunction"><a class="anchor" href="#_create_your_first_handlerfunction_routerfunction"></a>Create your first HandlerFunction + RouterFunction</h3>
<div class="paragraph">
<p>First, create a <code>QuoteHandler</code> class and mark is as a <code>@Component</code>;this class will have all our handler functions as methods.
Now create a <code>hello</code> handler function in that class that always returns "text/plain" HTTP responses with "Hello Spring!" as body.</p>
</div>
<div class="paragraph">
<p>To route requests to that handler, you need to expose a <code>RouterFunction</code> to Spring Boot.
Create a <code>QuoteRouter</code> configuration class (i.e. annotated with <code>@Configuration</code>)
that creates a bean of type <code>RouterFunction&lt;ServerResponse&gt;</code>.</p>
</div>
<div class="paragraph">
<p>Modify that class so that GET requests to <code>"/hello"</code> are routed to the handler you just implemented.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
Since <code>QuoteHandler</code> is a component, you can inject it in <code>@Bean</code> methods as a method parameter.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Your application should now behave like this:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-bash" data-lang="bash">$ curl http://localhost:8081/hello -i
HTTP/1.1 200 OK
transfer-encoding: chunked
Content-Type: text/plain;charset=UTF-8

Hello Spring!%</code></pre>
</div>
</div>
<div class="paragraph">
<p>Once done, add another endpoint:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>with a HandlerFunction <code>echo</code> that echoes the request body in the response, as "text/plain"</p>
</li>
<li>
<p>and an additional route in our existing <code>RouterFunction</code> that accepts POST requests on
<code>"/echo"</code> with a "text/plain" body and returns responses with the same content type.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>You can also use this new endpoint with:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-bash" data-lang="bash">$ curl http://localhost:8081/echo -i -d "WebFlux workshop" -H "Content-Type: text/plain"
HTTP/1.1 200 OK
transfer-encoding: chunked
Content-Type: text/plain

WebFlux workshop%</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_expose_the_flux_quotes_as_a_web_service"><a class="anchor" href="#_expose_the_flux_quotes_as_a_web_service"></a>Expose the Flux&lt;Quotes&gt; as a web service</h3>
<div class="paragraph">
<p>First, let&#8217;s inject our <code>QuoteGenerator</code> instance in our <code>QuoteHandler</code>, instantiate
a <code>Flux&lt;Quote&gt;</code> from it that emits a <code>Quote</code> every 200 msec and can be <strong>shared</strong> between
multiple subscribers (look at the <code>Flux</code> operators for that). This instance should be kept
as an attribute for reusability.</p>
</div>
<div class="paragraph">
<p>Now create a <code>streamQuotes</code> handler that streams those generated quotes
with the <code>"application/stream+json"</code> content type. Add the corresponding part in the <code>RouterFunction</code>,
on the <code>"/quotes"</code> endpoint.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-bash" data-lang="bash">$ curl http://localhost:8081/quotes -i -H "Accept: application/stream+json"
HTTP/1.1 200 OK
transfer-encoding: chunked
Content-Type: application/stream+json

{"ticker":"CTXS","price":84.0,"instant":1494841666.633000000}
{"ticker":"DELL","price":67.1,"instant":1494841666.834000000}
{"ticker":"GOOG","price":869,"instant":1494841667.034000000}
{"ticker":"MSFT","price":66.5,"instant":1494841667.231000000}
{"ticker":"ORCL","price":46.13,"instant":1494841667.433000000}
{"ticker":"RHT","price":86.9,"instant":1494841667.634000000}
{"ticker":"VMW","price":93.7,"instant":1494841667.833000000}</code></pre>
</div>
</div>
<div class="paragraph">
<p>Let&#8217;s now create a variant of that — instead of streaming all values (with an infinite stream), we can
now take the last "n" elements of that <code>Flux</code> and return those as a collection of Quotes with
the content type <code>"application/json"</code>. Note that you should take the requested number of Quotes
from the request itself, with the query parameter named <code>"size"</code> (or pick <code>10</code> as the default size
if none was provided).</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-bash" data-lang="bash">curl http://localhost:8081/quotes -i -H "Accept: application/json"
HTTP/1.1 200 OK
transfer-encoding: chunked
Content-Type: application/json

[{"ticker":"CTXS","price":85.8,"instant":1494842241.716000000},{"ticker":"DELL","price":64.69,"instant":1494842241.913000000},{"ticker":"GOOG","price":856.5,"instant":1494842242.112000000},{"ticker":"MSFT","price":68.2,"instant":1494842242.317000000},{"ticker":"ORCL","price":47.4,"instant":1494842242.513000000},{"ticker":"RHT","price":85.6,"instant":1494842242.716000000},{"ticker":"VMW","price":96.1,"instant":1494842242.914000000},{"ticker":"CTXS","price":85.5,"instant":1494842243.116000000},{"ticker":"DELL","price":64.88,"instant":1494842243.316000000},{"ticker":"GOOG","price":889,"instant":1494842243.517000000}]%</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_integration_tests_with_webtestclient"><a class="anchor" href="#_integration_tests_with_webtestclient"></a>Integration tests with WebTestClient</h3>
<div class="paragraph">
<p>Spring WebFlux (actually the <code>spring-test</code> module) includes a <code>WebTestClient</code>
that can be used to test WebFlux server endpoints with or without a running server.
Tests without a running server are comparable to MockMvc from Spring MVC where mock request
and response are used instead of connecting over the network using a socket.
The WebTestClient however can also perform tests against a running server.</p>
</div>
<div class="paragraph">
<p>You can check that your last endpoint is working properly with the following
integration test:</p>
</div>
<div class="listingblock">
<div class="title">stock-quotes/src/test/java/io/spring/workshop/stockquotes/StockQuotesApplicationTests.java</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-java" data-lang="java">package io.spring.workshop.stockquotes;

import java.util.List;

import org.junit.Test;
import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.reactive.server.WebTestClient;

import static org.assertj.core.api.Assertions.assertThat;

@RunWith(SpringRunner.class)
//  We create a `@SpringBootTest`, starting an actual server on a `RANDOM_PORT`
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class StockQuotesApplicationTests {

	// Spring Boot will create a `WebTestClient` for you,
	// already configure and ready to issue requests against "localhost:RANDOM_PORT"
	@Autowired
	private WebTestClient webTestClient;

	@Test
	public void fetchQuotes() {
		webTestClient
				// We then create a GET request to test an endpoint
				.get().uri("/quotes?size=20")
				.accept(MediaType.APPLICATION_JSON)
				.exchange()
				// and use the dedicated DSL to test assertions against the response
				.expectStatus().isOk()
				.expectHeader().contentType(MediaType.APPLICATION_JSON)
				.expectBodyList(Quote.class)
				.hasSize(20)
				// Here we check that all Quotes have a positive price value
				.consumeWith(allQuotes -&gt;
						assertThat(allQuotes.getResponseBody())
								.allSatisfy(quote -&gt; assertThat(quote.getPrice()).isPositive()));
	}

	@Test
	public void fetchQuotesAsStream() {
		List&lt;Quote&gt; result = webTestClient
				// We then create a GET request to test an endpoint
				.get().uri("/quotes")
				// this time, accepting "application/stream+json"
				.accept(MediaType.APPLICATION_STREAM_JSON)
				.exchange()
				// and use the dedicated DSL to test assertions against the response
				.expectStatus().isOk()
				.expectHeader().contentType(MediaType.APPLICATION_STREAM_JSON)
				.returnResult(Quote.class)
				.getResponseBody()
				.take(30)
				.collectList()
				.block();

		assertThat(result).allSatisfy(quote -&gt; assertThat(quote.getPrice()).isPositive());
	}

}</code></pre>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_trading_service_application"><a class="anchor" href="#_trading_service_application"></a>Trading Service application</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_create_this_application_2"><a class="anchor" href="#_create_this_application_2"></a>Create this application</h3>
<div class="paragraph">
<p>Go to <code><a href="https://start.spring.io" class="bare">https://start.spring.io</a></code> and create a Maven project with Spring Boot 2.0.2.RELEASE,
with groupId <code>io.spring.workshop</code> and artifactId <code>trading-service</code>. Select the <code>Reactive Web</code>
, <code>Devtools</code>, <code>Thymeleaf</code> and <code>Reactive Mongo</code> Boot starters.
Unzip the given file into a directory and import that application into your IDE.</p>
</div>
</div>
<div class="sect2">
<h3 id="_use_tomcat_as_a_web_engine"><a class="anchor" href="#_use_tomcat_as_a_web_engine"></a>Use Tomcat as a web engine</h3>
<div class="paragraph">
<p>By default, <code>spring-boot-starter-webflux</code> transitively brings <code>spring-boot-starter-reactor-netty</code>
and Spring Boot auto-configures Reactor Netty as a web server. For this application, we&#8217;ll use
Tomcat as an alternative.</p>
</div>
<div class="listingblock">
<div class="title">trading-service/pom.xml</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-xml" data-lang="xml">		&lt;dependency&gt;
			&lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
			&lt;artifactId&gt;spring-boot-starter-tomcat&lt;/artifactId&gt;
		&lt;/dependency&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>Note that Spring Boot supports as well Undertow and Jetty.</p>
</div>
</div>
<div class="sect2">
<h3 id="_use_a_reactive_datastore"><a class="anchor" href="#_use_a_reactive_datastore"></a>Use a reactive datastore</h3>
<div class="paragraph">
<p>In this application, we&#8217;ll use a MongoDB datastore with its reactive driver;
for this workshop, we&#8217;ll use an in-memory instance of MongoDB. So add the following:</p>
</div>
<div class="listingblock">
<div class="title">trading-service/pom.xml</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-xml" data-lang="xml">		&lt;dependency&gt;
			&lt;groupId&gt;de.flapdoodle.embed&lt;/groupId&gt;
			&lt;artifactId&gt;de.flapdoodle.embed.mongo&lt;/artifactId&gt;
		&lt;/dependency&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>We&#8217;d like to manage <code>TradingUser</code> with our datastore.</p>
</div>
<div class="listingblock">
<div class="title">trading-service/src/main/java/io/spring/workshop/tradingservice/TradingUser.java</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-java" data-lang="java">package io.spring.workshop.tradingservice;

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Document
public class TradingUser {

	@Id
	private String id;

	private String userName;

	private String fullName;

	public TradingUser() {
	}

	public TradingUser(String id, String userName, String fullName) {
		this.id = id;
		this.userName = userName;
		this.fullName = fullName;
	}

	public TradingUser(String userName, String fullName) {
		this.userName = userName;
		this.fullName = fullName;
	}

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getUserName() {
		return userName;
	}

	public void setUserName(String userName) {
		this.userName = userName;
	}

	public String getFullName() {
		return fullName;
	}

	public void setFullName(String fullName) {
		this.fullName = fullName;
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) return true;
		if (o == null || getClass() != o.getClass()) return false;

		TradingUser that = (TradingUser) o;

		if (!id.equals(that.id)) return false;
		return userName.equals(that.userName);
	}

	@Override
	public int hashCode() {
		int result = id.hashCode();
		result = 31 * result + userName.hashCode();
		return result;
	}
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>Now create a <code>TradingUserRepository</code> interface that extends <code>ReactiveMongoRepository</code>.
Add a <code>findByUserName(String userName)</code> method that returns a single <code>TradingUser</code> in a reactive fashion.</p>
</div>
<div class="paragraph">
<p>We&#8217;d like to insert users in our datastore when the application starts up. For that, create a <code>UsersCommandLineRunner</code>
component that implements Spring Boot&#8217;s <code>CommandLineRunner</code>. In the <code>run</code> method, use the reactive repository
to insert <code>TradingUser</code> instances in the datastore.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
Since the <code>run</code> method returns void, it expects a blocking implementation. This is why you should use the
<code>blockLast(Duration)</code> operator on the <code>Flux</code> returned by the repository when inserting data.
You can also <code>then().block(Duration)</code> to turn that <code>Flux</code> into a <code>Mono&lt;Void&gt;</code> that waits for completion.
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="_create_a_json_web_service"><a class="anchor" href="#_create_a_json_web_service"></a>Create a JSON web service</h3>
<div class="paragraph">
<p>We&#8217;re now going to expose <code>TradingUser</code> through a Controller.
First, create a <code>UserController</code> annotated with <code>@RestController</code>.
Then add two new Controller methods in order to handle:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>GET requests to  <code>"/users"</code>, returning all <code>TradingUser</code> instances, serializing them with content-type <code>"application/json"</code></p>
</li>
<li>
<p>GET requests to  <code>"/users/{username}"</code>, returning a single <code>TradingUser</code> instance, serializing it with content-type <code>"application/json"</code></p>
</li>
</ul>
</div>
<div class="paragraph">
<p>You can now validate your implementation with the following test:</p>
</div>
<div class="listingblock">
<div class="title">trading-service/src/test/java/io/spring/workshop/tradingservice/UserControllerTests.java</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-java" data-lang="java">package io.spring.workshop.tradingservice;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.BDDMockito;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.reactive.server.WebTestClient;

@RunWith(SpringRunner.class)
@WebFluxTest(UserController.class)
public class UserControllerTests {

  @Autowired
  private WebTestClient webTestClient;

  @MockBean
  private TradingUserRepository repository;

  @Test
  public void listUsers() {
    TradingUser juergen = new TradingUser("1", "jhoeller", "Juergen Hoeller");
    TradingUser andy = new TradingUser("2", "wilkinsona", "Andy Wilkinson");

    BDDMockito.given(this.repository.findAll())
        .willReturn(Flux.just(juergen, andy));

    this.webTestClient.get().uri("/users").accept(MediaType.APPLICATION_JSON)
        .exchange()
        .expectBodyList(TradingUser.class)
        .hasSize(2)
        .contains(juergen, andy);

  }

  @Test
  public void showUser() {
    TradingUser juergen = new TradingUser("1", "jhoeller", "Juergen Hoeller");

    BDDMockito.given(this.repository.findByUserName("jhoeller"))
        .willReturn(Mono.just(juergen));

    this.webTestClient.get().uri("/users/jhoeller").accept(MediaType.APPLICATION_JSON)
        .exchange()
        .expectBody(TradingUser.class)
        .isEqualTo(juergen);
  }

}</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_use_thymeleaf_to_render_html_views"><a class="anchor" href="#_use_thymeleaf_to_render_html_views"></a>Use Thymeleaf to render HTML views</h3>
<div class="paragraph">
<p>We already added the Thymeleaf Boot starter when we created our trading application.</p>
</div>
<div class="paragraph">
<p>First, let&#8217;s add a couple of WebJar dependencies to get static resources for our application:</p>
</div>
<div class="listingblock">
<div class="title">trading-service/pom.xml</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-xml" data-lang="xml">		&lt;dependency&gt;
			&lt;groupId&gt;org.webjars&lt;/groupId&gt;
			&lt;artifactId&gt;bootstrap&lt;/artifactId&gt;
			&lt;version&gt;3.3.7&lt;/version&gt;
		&lt;/dependency&gt;
		&lt;dependency&gt;
			&lt;groupId&gt;org.webjars&lt;/groupId&gt;
			&lt;artifactId&gt;highcharts&lt;/artifactId&gt;
			&lt;version&gt;5.0.8&lt;/version&gt;
		&lt;/dependency&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>We can now create HTML templates in our <code>src/main/resources/templates</code> folder and map them using controllers.</p>
</div>
<div class="listingblock">
<div class="title">trading-service/src/main/resources/templates/index.html</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-html" data-lang="html">&lt;!DOCTYPE html&gt;
&lt;html lang="en" xmlns:th="http://www.thymeleaf.org"&gt;
&lt;head&gt;
    &lt;meta charset="utf-8"/&gt;
    &lt;meta http-equiv="X-UA-Compatible" content="IE=edge"/&gt;
    &lt;meta name="viewport" content="width=device-width, initial-scale=1"/&gt;
    &lt;meta name="description" content="Spring WebFlux Workshop"/&gt;
    &lt;meta name="author" content="Violeta Georgieva and Brian Clozel"/&gt;
    &lt;title&gt;Spring Trading application&lt;/title&gt;
    &lt;link rel="stylesheet" href="/webjars/bootstrap/3.3.7/css/bootstrap-theme.min.css"/&gt;
    &lt;link rel="stylesheet" href="/webjars/bootstrap/3.3.7/css/bootstrap.min.css"/&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;nav class="navbar navbar-default"&gt;
    &lt;div class="container-fluid"&gt;
        &lt;div class="navbar-header"&gt;
            &lt;a class="navbar-brand" href="/"&gt;Spring Trading application&lt;/a&gt;
        &lt;/div&gt;
        &lt;div id="navbar" class="navbar-collapse collapse"&gt;
            &lt;ul class="nav navbar-nav"&gt;
                &lt;li class="active"&gt;&lt;a href="/"&gt;Home&lt;/a&gt;&lt;/li&gt;
                &lt;li&gt;&lt;a href="/quotes"&gt;Quotes&lt;/a&gt;&lt;/li&gt;
                &lt;li&gt;&lt;a href="/websocket"&gt;Websocket&lt;/a&gt;&lt;/li&gt;
            &lt;/ul&gt;
        &lt;/div&gt;
    &lt;/div&gt;
&lt;/nav&gt;
&lt;div class="container wrapper"&gt;
    &lt;h2&gt;Trading users&lt;/h2&gt;
    &lt;table class="table table-striped"&gt;
        &lt;thead&gt;
        &lt;tr&gt;
            &lt;th&gt;#&lt;/th&gt;
            &lt;th&gt;User name&lt;/th&gt;
            &lt;th&gt;Full name&lt;/th&gt;
        &lt;/tr&gt;
        &lt;/thead&gt;
        &lt;tbody&gt;
        &lt;tr th:each="user: ${users}"&gt;
            &lt;th scope="row" th:text="${user.id}"&gt;42&lt;/th&gt;
            &lt;td th:text="${user.userName}"&gt;janedoe&lt;/td&gt;
            &lt;td th:text="${user.fullName}"&gt;Jane Doe&lt;/td&gt;
        &lt;/tr&gt;
        &lt;/tbody&gt;
    &lt;/table&gt;
&lt;/div&gt;
&lt;script type="text/javascript" src="/webjars/jquery/1.11.1/jquery.min.js"&gt;&lt;/script&gt;
&lt;script type="text/javascript" src="/webjars/bootstrap/3.3.7/js/bootstrap.min.js"&gt;&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>As you can see in that template, we loop over the <code>"users"</code> attribute and write a row in our HTML table for each.</p>
</div>
<div class="paragraph">
<p>Let&#8217;s display those users in our application:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Create a <code>HomeController</code> Controller</p>
</li>
<li>
<p>Add a Controller method that handles GET requests to <code>"/"</code></p>
</li>
<li>
<p>Inject the Spring <code>Model</code> on that method and add a <code>"users"</code> attribute to it</p>
</li>
</ul>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
Spring WebFlux will resolve automatically <code>Publisher</code> instances before rendering the view,
there&#8217;s no need to involve blocking code at all!
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="_use_the_webclient_to_stream_json_to_the_browser"><a class="anchor" href="#_use_the_webclient_to_stream_json_to_the_browser"></a>Use the WebClient to stream JSON to the browser</h3>
<div class="paragraph">
<p>In this section, we&#8217;ll call our remote <code>stock-quotes</code> service to get Quotes from it, so we first need to:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>copy over the <code>Quote</code> class to this application</p>
</li>
<li>
<p>add the following template file to your application:</p>
</li>
</ul>
</div>
<div class="listingblock">
<div class="title">trading-service/src/main/resources/templates/quotes.html</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-html" data-lang="html">&lt;!DOCTYPE html&gt;
&lt;html lang="en" xmlns:th="http://www.thymeleaf.org"&gt;
&lt;head&gt;
    &lt;meta charset="utf-8"/&gt;
    &lt;meta http-equiv="X-UA-Compatible" content="IE=edge"/&gt;
    &lt;meta name="viewport" content="width=device-width, initial-scale=1"/&gt;
    &lt;meta name="description" content="Spring WebFlux Workshop"/&gt;
    &lt;meta name="author" content="Violeta Georgieva and Brian Clozel"/&gt;
    &lt;title&gt;Spring Trading application&lt;/title&gt;
    &lt;link rel="stylesheet" href="/webjars/bootstrap/3.3.7/css/bootstrap-theme.min.css"/&gt;
    &lt;link rel="stylesheet" href="/webjars/bootstrap/3.3.7/css/bootstrap.min.css"/&gt;
    &lt;link rel="stylesheet" href="/webjars/highcharts/5.0.8/css/highcharts.css"/&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;nav class="navbar navbar-default"&gt;
    &lt;div class="container-fluid"&gt;
        &lt;div class="navbar-header"&gt;
            &lt;a class="navbar-brand" href="/"&gt;Spring Trading application&lt;/a&gt;
        &lt;/div&gt;
        &lt;div id="navbar" class="navbar-collapse collapse"&gt;
            &lt;ul class="nav navbar-nav"&gt;
                &lt;li&gt;&lt;a href="/"&gt;Home&lt;/a&gt;&lt;/li&gt;
                &lt;li class="active"&gt;&lt;a href="/quotes"&gt;Quotes&lt;/a&gt;&lt;/li&gt;
                &lt;li&gt;&lt;a href="/websocket"&gt;Websocket&lt;/a&gt;&lt;/li&gt;
            &lt;/ul&gt;
        &lt;/div&gt;
    &lt;/div&gt;
&lt;/nav&gt;
&lt;div class="container wrapper"&gt;
    &lt;div id="chart" style="height: 400px; min-width: 310px"&gt;&lt;/div&gt;
&lt;/div&gt;
&lt;script type="text/javascript" src="/webjars/jquery/1.11.1/jquery.min.js"&gt;&lt;/script&gt;
&lt;script type="text/javascript" src="/webjars/highcharts/5.0.8/highcharts.js"&gt;&lt;/script&gt;
&lt;script type="text/javascript" src="/webjars/bootstrap/3.3.7/js/bootstrap.min.js"&gt;&lt;/script&gt;
&lt;script type="text/javascript"&gt;

    // Setting up the chart
    var chart = new Highcharts.Chart('chart', {
        title: {
            text: 'My Stock Portfolio'
        },
        yAxis: {
            title: {
                text: 'Stock Price'
            }
        },
        legend: {
            layout: 'vertical',
            align: 'right',
            verticalAlign: 'middle'
        },
        xAxis: {
            type: 'datetime'
        },
        series: [{
            name: 'CTXS',
            data: []
        }, {
            name: 'MSFT',
            data: []
        }, {
            name: 'ORCL',
            data: []
        }, {
            name: 'RHT',
            data: []
        }, {
            name: 'VMW',
            data: []
        }, {
            name: 'DELL',
            data: []
        }]
    });

    // This function adds the given data point to the chart
    var appendStockData = function (quote) {
        chart.series
            .filter(function (serie) {
                return serie.name === quote.ticker
            })
            .forEach(function (serie) {
                var shift = serie.data.length &gt; 40;
                serie.addPoint([Date.parse(quote.instant), quote.price], true, shift);
            });
    };

    // The browser connects to the server and receives quotes using ServerSentEvents
    // those quotes are appended to the chart as they're received
    var stockEventSource = new EventSource("/quotes/feed");
    stockEventSource.onmessage = function (e) {
        appendStockData(JSON.parse(e.data));
    };
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>As you can see in this template file, loading that HTML page will cause the browser to send a request
the server for <code>Quotes</code> using the Server Sent Event transport.</p>
</div>
<div class="paragraph">
<p>Now create a <code>QuotesController</code> annotated with <code>@Controller</code> and add two methods.
One that renders the <code>quotes.html</code> template for incoming <code>"GET /quotes"</code> requests.
The other should response to <code>"GET /quotes/feed"</code> requests with the <code>"text/event-stream"</code> content-type,
with a <code>Flux&lt;Quote&gt;</code> as the response body. This data is already server by the <code>stock-quotes</code> application
, so you can use a <code>WebClient</code> to request the remote web service to retrieve that <code>Flux</code>.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
You should avoid making a request to the <code>stock-quotes</code> service for every browser connecting to
that page — for that, you can use the <code>Flux.share()</code> operator.
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="_create_and_configure_a_websockethandler"><a class="anchor" href="#_create_and_configure_a_websockethandler"></a>Create and Configure a WebSocketHandler</h3>
<div class="paragraph">
<p>WebFlux includes functional reactive WebSocket client and server support.</p>
</div>
<div class="paragraph">
<p>On the server side there are two main components: <code>WebSocketHandlerAdapter</code> will handle the incoming
requests by delegating to the configured <code>WebSocketService</code> and <code>WebSocketHandler</code> will be responsible
to handle WebSocket session.</p>
</div>
<div class="paragraph">
<p>Take a look at the code samples in
<a href="http://docs.spring.io/spring-framework/docs/5.0.6.RELEASE/spring-framework-reference/web.html#web-reactive-websocket-support">Reactive WebSocket Support documentation</a></p>
</div>
<div class="paragraph">
<p>First, create an <code>EchoWebSocketHandler</code> class; it has to implement <code>WebSocketHandler</code>.
Now implement <code>handle(WebSocketSession session)</code> method. The handler echoes the incoming messages with a delay of 1s.</p>
</div>
<div class="paragraph">
<p>To route requests to that handler, you need to map the above WebSocket handler to a specific URL: here, <code>"/websocket/echo"</code>.
Create a <code>WebSocketRouter</code> configuration class (i.e. annotated with <code>@Configuration</code>) that creates a bean of type <code>HandlerMapping</code>.
Create one additional bean of type <code>WebSocketHandlerAdapter</code> which will delegate the processing of
the incoming request to the default <code>WebSocketService</code> which is <code>HandshakeWebSocketService</code>.</p>
</div>
<div class="paragraph">
<p>Now create a <code>WebSocketController</code> annotated with @Controller and add a method that renders the
<code>websocket.html</code> template for incoming <code>"GET /websocket"</code> requests.</p>
</div>
<div class="paragraph">
<p>Add the following template file to your application:</p>
</div>
<div class="listingblock">
<div class="title">trading-service/src/main/resources/templates/websocket.html</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-html" data-lang="html">&lt;!DOCTYPE html&gt;
&lt;html lang="en" xmlns:th="http://www.thymeleaf.org"&gt;
&lt;head&gt;
    &lt;meta charset="utf-8"/&gt;
    &lt;meta http-equiv="X-UA-Compatible" content="IE=edge"/&gt;
    &lt;meta name="viewport" content="width=device-width, initial-scale=1"/&gt;
    &lt;meta name="description" content="Spring WebFlux Workshop"/&gt;
    &lt;meta name="author" content="Violeta Georgieva and Brian Clozel"/&gt;
    &lt;title&gt;Spring Trading application&lt;/title&gt;
    &lt;link rel="stylesheet" href="/webjars/bootstrap/3.3.7/css/bootstrap-theme.min.css"/&gt;
    &lt;link rel="stylesheet" href="/webjars/bootstrap/3.3.7/css/bootstrap.min.css"/&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;nav class="navbar navbar-default"&gt;
    &lt;div class="container-fluid"&gt;
        &lt;div class="navbar-header"&gt;
            &lt;a class="navbar-brand" href="/"&gt;Spring Trading application&lt;/a&gt;
        &lt;/div&gt;
        &lt;div id="navbar" class="navbar-collapse collapse"&gt;
            &lt;ul class="nav navbar-nav"&gt;
                &lt;li&gt;&lt;a href="/"&gt;Home&lt;/a&gt;&lt;/li&gt;
                &lt;li&gt;&lt;a href="/quotes"&gt;Quotes&lt;/a&gt;&lt;/li&gt;
                &lt;li class="active"&gt;&lt;a href="/websocket"&gt;Websocket&lt;/a&gt;&lt;/li&gt;
            &lt;/ul&gt;
        &lt;/div&gt;
    &lt;/div&gt;
&lt;/nav&gt;
&lt;div class="container wrapper"&gt;
    &lt;h2&gt;Websocket Echo&lt;/h2&gt;
    &lt;form class="form-inline"&gt;
        &lt;div class="form-group"&gt;
            &lt;input class="form-control" type="text" id="input" value="type something"&gt;
            &lt;input class="btn btn-default" type="submit" id="button" value="Send"/&gt;
        &lt;/div&gt;
    &lt;/form&gt;
    &lt;div id="output"&gt;&lt;/div&gt;
&lt;/div&gt;
&lt;script type="text/javascript" src="/webjars/jquery/1.11.1/jquery.min.js"&gt;&lt;/script&gt;
&lt;script type="text/javascript" src="/webjars/bootstrap/3.3.7/js/bootstrap.min.js"&gt;&lt;/script&gt;
&lt;script type="text/javascript"&gt;
    $(document).ready(function () {
        if (!("WebSocket" in window)) WebSocket = MozWebSocket;
        var socket = new WebSocket("ws://localhost:8080/websocket/echo");

        socket.onopen = function (event) {
            var newMessage = document.createElement('p');
            newMessage.textContent = "-- CONNECTED";
            document.getElementById('output').appendChild(newMessage);

            socket.onmessage = function (e) {
                var newMessage = document.createElement('p');
                newMessage.textContent = "&lt;&lt; SERVER: " + e.data;
                document.getElementById('output').appendChild(newMessage);
            }

            $("#button").click(function (e) {
                e.preventDefault();
                var message = $("#input").val();
                socket.send(message);
                var newMessage = document.createElement('p');
                newMessage.textContent = "&gt;&gt; CLIENT: " + message;
                document.getElementById('output').appendChild(newMessage);
            });
        }
    });
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_integration_tests_with_websocketclient"><a class="anchor" href="#_integration_tests_with_websocketclient"></a>Integration tests with WebSocketClient</h3>
<div class="paragraph">
<p><code>WebSocketClient</code> included in Spring WebFlux can be used to test your WebSocket endpoints.</p>
</div>
<div class="paragraph">
<p>You can check that your WebSocket endpoint, created in the previous section, is working properly with the
following integration test:</p>
</div>
<div class="listingblock">
<div class="title">trading-service/src/test/java/io/spring/workshop/tradingservice/websocket/EchoWebSocketHandlerTests.java</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-java" data-lang="java">package io.spring.workshop.tradingservice.websocket;

import static org.junit.Assert.assertEquals;

import java.net.URI;
import java.net.URISyntaxException;
import java.time.Duration;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.web.server.LocalServerPort;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.web.reactive.socket.WebSocketMessage;
import org.springframework.web.reactive.socket.client.StandardWebSocketClient;
import org.springframework.web.reactive.socket.client.WebSocketClient;

import reactor.core.publisher.Flux;
import reactor.core.publisher.ReplayProcessor;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class EchoWebSocketHandlerTests {

	@LocalServerPort
	private String port;

	@Test
	public void echo() throws Exception {
		int count = 4;
		Flux&lt;String&gt; input = Flux.range(1, count).map(index -&gt; "msg-" + index);
		ReplayProcessor&lt;Object&gt; output = ReplayProcessor.create(count);

		WebSocketClient client = new StandardWebSocketClient();
		client.execute(getUrl("/websocket/echo"),
				session -&gt; session
						.send(input.map(session::textMessage))
						.thenMany(session.receive().take(count).map(WebSocketMessage::getPayloadAsText))
						.subscribeWith(output)
						.then())
				.block(Duration.ofMillis(5000));

		assertEquals(input.collectList().block(Duration.ofMillis(5000)), output.collectList().block(Duration.ofMillis(5000)));
	}

	protected URI getUrl(String path) throws URISyntaxException {
		return new URI("ws://localhost:" + this.port + path);
	}
}</code></pre>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_additional_resources"><a class="anchor" href="#_additional_resources"></a>Additional Resources</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Talks on Spring Reactive:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="https://www.youtube.com/watch?v=rdgJ8fOxJhc">Reactive Web Applications with Spring 5 (Rossen Stoyanchev)</a></p>
</li>
<li>
<p><a href="https://www.youtube.com/watch?v=Cj4foJzPF80">Developing Reactive applications with Reactive Streams and Java 8 (B.Clozel, S.Deleuze)</a></p>
</li>
</ul>
</div>
</div>
</div>
</div>
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